An engine may include a plurality of variable valve actuators that allow one or more engine cylinders to be activated or deactivated between engine cycles. In some engines, the engine cylinders that are deactivated may vary each engine cycle so that each engine cylinder is deactivated a same number of times as other cylinders of the engine over a plurality of engine cycles. By deactivating engine cylinders in this way, engine pumping losses may be reduced and operating conditions of engine cylinders may be more uniform. However, over the course of operating the engine over a significant amount of time and driving distance, the engine valve actuators may change state so many times that they degrade, thereby making engine cylinder deactivation less reliable. This may be especially true for engines that switch which engine cylinders are deactivated each engine cycle or each engine event since each valve actuator of each engine cylinder may be repeatedly switched from operating a valve to not operating the valve even when engine load is constant.
The inventor herein has recognized the above-mentioned issues and has developed an engine control method, comprising: deactivating engine cylinders via a controller according to a first cylinder deactivation strategy in response to an actual total number of valve actuator state changes being less than a first threshold; and deactivating the engine cylinders via the controller according to a second cylinder deactivation strategy in response to an actual total number of valve actuator state changes being greater than a second threshold.
By changing between two or more cylinder deactivation strategies in response to an actual total number of valve actuator state changes, it may be possible to provide the technical result of extending an operating time of engine valve actuators. In particular, valve actuators may have a finite number of state changes which they are expected to operate with a low probability of degradation. If the valve actuators continue to change state at a same rate after the finite number of state changes, the possibility of valve actuator degradation may increase. Nevertheless, the rate at which valve actuators change state may be reduced by deactivating fixed groups of cylinders instead of rotating or varying which cylinders are deactivated each engine cycle. The rate at which a valve actuator changes state may be reduced when cylinders are deactivated in fixed groups because valve actuators do not have to change state each engine cycle as compared to strategies where valve actuators can change state each engine cycle. Therefore, a second valve strategy where cylinders are deactivated in a fixed group may be substituted or combined with a first strategy where cylinders are deactivated on a rotating basis (e.g., in a first engine cycle, engine cylinder number one may be deactivated while engine cylinders two, three, and four are active; in a second engine cycle immediately following the first engine cycle, engine cylinder number two may be deactivated while engine cylinders one, three, and four are active; in a third engine cycle immediately following the second engine cycle, engine cylinder number three may be deactivated while engine cylinders one, two, and four are active, and so on) to reduce valve actuator state changes, thereby extending valve actuator operating time.
The present description may provide several advantages. In particular, the approach may increase an amount of time a valve actuator may operate without degradation. Further, the approach provides progressive actions that act to extend valve actuator usefulness while still enabling cylinder deactivation. In addition, the approach may deactivate cylinder deactivation so that cylinder operation may be maintained even though a valve actuator is approaching conditions where valve actuator degradation is expected.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.